Kidney disease is ranked fourth among the major diseases in the United States afflicting over 20 million Americans. More than 90,000 patients die each year because of kidney diseases. In recent years the number of chronic kidney failure patients has increased about 11 percent annually. About 80,000 Americans on dialysis die of various complications each year and more than 27,000 are on waiting lists for kidney transplants each year with only about 11,000 of these patients receiving transplants.
Nearly 250,000 Americans suffer from end stage renal disease (ESRD), which is the final stage in chronic renal failure. Currently hemo- or peritoneal-dialysis and renal transplant are the only treatment modalities. However, the economic costs of these treatment modalities is extremely high. For example, in 1996 in the United States alone, the annual cost of ESRD treatment was over 14 billion dollars. In developing and underdeveloped countries with low health care budgets, ESRD patients are deprived access to such treatments due to their high costs. Accordingly, there is a need for alternative modalities of treatment for uremia.
A number of treatment attempts have been based on the use of the bowel as a substitute for kidney function. During a normal digestive process the gastrointestinal tract delivers nutrients and water to the bloodstream and eliminates waste products and undigested materials through the bowel. The intestinal wall regulates absorption of nutrients, electrolytes, water and certain digestive aiding substances such as bile acids. The intestinal wall also acts as a semipermeable membrane allowing small molecules to pass from the intestinal tract into the bloodstream and preventing larger molecules from entering the circulation.
Nitrogenous wastes such as urea, creatinine and uric acid, along with several other small and medium molecular weight compounds, flow into the small intestine and equilibrate across the small intestine epithelium. Studies of intestinal dialysis have shown a daily flow of 71 grams of urea, 2.9 grams of creatinine, 2.5 grams of uric acid and 2.0 grams of phosphate into the intestinal fluid (Sparks, R. E. Kidney Int. Suppl. 1975 Suppl 3, 7:373 376). Accordingly, various invasive and noninvasive attempts including external gut fistula, intestinal dialysis, induced diarrhea, and administration of oral sorbents and/or encapsulated urease enzyme have been made to extract uremic waste from the gastrointestinal tract (Twiss, E. E. and Kolff, W. J. JAMA 1951 146:1019-1022; Clark et al. Trans. Am. Soc. Artif. Intrn. Organs 1962 8:246-251; Pateras et al. Trans. Am. Soc. Artif. Intrn. Organs 1965 11:292-295; Shimizu et al. Chemical Abstracts 1955 103:129004; Kjellstrand et al. Trans. Am. Soc. Artif. Intern. Organs 1981 27:24-29; and Kolff, W. J. Kidney Int. 1976 10:S211-S214).
Activated charcoal was the first oral sorbent studied for treatment of uremia. Activated charcoal is a highly porous material with large surface area obtained by carbonization of organic materials such as wood, petroleum, coal, peat, and coconut shell followed by activation with steam, carbon dioxide or chemicals such as zinc chloride. Solute adsorption by activated charcoal depends on a number of factors including concentration of the solute in bulk phase, chemical nature of the solute, temperature, and pH. In general, however, activated charcoal binds more avidly to non-polar solutes than polar solutes. In in vivo studies, 190 grams of activated charcoal was required to remove 450 mg of creatinine (Goldenhersh et al. Kidney Int. 1976 10:S251-S253). This reduced efficacy is believed to be due to adsorption of other lipophilic compounds such as cholesterol and related bile acids (Kolff, W. J. Kidney Int. 1976 10:S211-S214; Goldenhersh et al. Kidney Int. 1976 10:S251-S253). Microencapsulation of activated charcoal has been shown to reduce the amount of charcoal needed to 50 grams (Goldenhersh et al. Kidney Int. 1976 10:S251-S253).
AST-120, a proprietary and specially-prepared, coated material of porous carbon of 0.2 to 0.4 mm, has been demonstrated to be a more effective charcoal based adsorbent. A dose of 3.2 to 7.2 grams to uremic patients has been disclosed to delay the rise in serum level of creatinine and delay the onset of renal dysfunction in nephrectomized rats as well as 27 uremic patients (Owadu, A. and Shiigai, T. Am. J. Nephrol. 1996 16(2):124-7; and Okada, K. and Takahashi, S. Nephrol. Dial. Transplant. 1995 10(5):671-6).
Several studies have also shown that ingestion of dialdehyde starch, also referred to as oxystarch, resulted in increased excretion of non-protein nitrogen (Giordano et al. Bull. Soc. Ital. Biol. Sper. 1968 44:2232-2234; Giordano et al. Kidney Int. 1976 10:S266-S268: Friedman et al. Proc. Clin. Dia. Trans. Forum 1977 7:183-184). Unlike activated charcoal where adsorption of the uremic solute is a physical process easily reversible, dialdehyde starch binds urea and ammonia via chemisorption involving covalent binding to the two-aldehyde groups. However, like activated charcoal, ingestion of very large amounts of about 30-50 grams only removed 1.5 grams of urea. Additional studies wherein dialdehyde starch and activated charcoal were both ingested demonstrated some improvement in uremic waste removal (Friedman et al. Proc. Clin. Dia. Trans. Forum 1977 7:183-184). Further, coating of dialdehyde starch with gelatin and albumin resulted in 6-fold better sorbency as compared to uncoated dialdehyde starch (Shimizu et al. Chemical Abstracts 1982 97:222903). More recently, retardation of progression of chronic renal failure has been shown following administration of chitosan coated oxycellulose or cellulose dialdehyde (Nagano et al. Medline Abstract UI 96058336 1995).
Locust bean gum, a naturally available carbohydrate based polymeric oral sorbent, when administered at 25 grams/day in cottonseed oil to uremic patients, was also demonstrated to remove significant amounts of urea, creatinine and phosphate. Further, locust bean gum adsorbs about 10 times its own weight in water (Yatzidis et al. Clinical Nephrology 1979 11:105-106).
Dietary supplementation with gum arabic fiber has also been demonstrated to increase fecal nitrogen excretion and lower serum nitrogen concentration in chronic renal failure patients on low protein diets (Bliss et al. Am. J. Clin. Nutr. 1996 63:392-98).
Encapsulated urease enzyme has also been investigated as a nonabsorbable oral sorbent for binding ammonia. In early studies zirconium phosphate and encapsulated urease enzyme were used as a non-absorbable oral sorbent for binding ammonia (Kjellstrand et al. Trans. Am. Soc. Artif. Intern. Organs 1981 27:24-29). A liquid-membrane capsule device with encapsulated urease to hydrolyze urea to ammonia and citric acid to neutralize the ammonia has also been investigated (Asher et al. Kidney Int. 1976 10:S254-S258). Soil bacteria has also been used to recycle urea as metabolically useful amino acids (Setala, K. Kidney Int. Suppl. 1978 8:S194-202). In addition, genetically engineered E. herbicola cells have been encapsulated and demonstrated to convert ammonia into usable amino acids for the cells before being eliminated via the bowel. Microencapsulated genetically engineered E. coli DH5 cells have also been shown to be effective in removal of urea and ammonia in an in vitro system and in a uremic rat animal model (Prakash, S. and Chang, T. M. S. Biotechnology and Bioengineering 1995 46:621-26; and Prakash, S. and Chang, T. M. S. Nature Med. 1996 2:883-887).
For effective treatment of renal failure, however, it has been estimated that at least 6.0 grams of urea, 0.5 grams of creatinine, 0.5 grams of uric acid and 1.2 grams of phosphate must be removed. Accordingly, there is a need for more effective treatments which remove multiple uremic toxins at higher concentrations to alleviate the symptoms of uremia in patients.
The present invention relates to compositions and methods of using these compositions to alleviate the symptoms of uremia. Compositions of the present invention comprise a mixture of sorbents with specific adsorption affinities for uremic toxins such as ammonia, urea, creatinine, phenols, indoles, and middle molecular weight molecules. These compositions also comprise a bacterial source which metabolizes urea and ammonia. These compositions are microencapsulated and/or enteric coated to deliver the sorbent and bacterial source to the ileal and colonic regions wherein maximal resorption of uremic solutes and other molecules occurs.
An object of the present invention is to provide microencapsulated and/or enteric coated compositions which comprise a mixture of sorbents with specific adsorption affinities for uremic toxins including ammonia, urea, creatinine, phenols, indoles, and middle molecular weight molecules; and a bacterial source which metabolizes urea and ammonia for use in patients in the alleviation of symptoms associated with uremia.
Another object of the present invention is to provide a method of alleviating symptoms of uremia in a patient which comprises administering orally to a patient suffering from uremia a microencapsulated and/or enteric coated composition comprising a mixture of sorbents with specific adsorption affinities for uremic toxins including ammonia, urea, creatinine, phenols, indoles, and middle molecules; and a bacterial source which metabolizes urea and ammonia.
In kidney failure there is a decrease in the glomerular filtration rate and the kidneys are unable to maintain homeostasis of the blood. Homeostatic balance of water, sodium, potassium, calcium and other salts is no longer possible and nitrogenous wastes are not excreted. Retention of water causes edema and as the concentration of hydrogen ions increases, acidosis develops. Nitrogenous wastes accumulate and a condition referred to as uremia develops in the blood and tissue. Uremic toxins can be defined as solutes that: (I) are normally excreted by healthy kidneys, (ii) accumulate progressively during the development of renal failure so that their concentration increases, and (iii) inhibit various physiologic and biochemical functions; as a whole, they contribute to a complex set of clinical symptoms that comprise the Uremic Syndrome. Examples of uremic toxins include, but are not limited to, ammonia, urea, creatinine, phenols, indoles, and middle molecular weight molecules. More specifically, in uremia, the concentration of serum creatinine, blood urea nitrogen (BUN), uric acid, and guanidino compounds such as N-methyl guanidine (NMG) and guanidino succinic acid (GSA) are significantly altered with accompanying abnormalities in acid-base equilibrium, electrolytes and water retention. In addition, there are several known and unknown substances of low and middle molecular weight which have been identified as uremic toxins which also accumulate. If untreated the acidosis and uremia can cause coma and eventually death.
Further, as a result of poor clearance of waste products of metabolism, there are some compensatory as well as adaptive processes, which further complicate the condition. For example, bacterial overgrowth of the normal flora of the gut occurs when kidney function is reduced to less than 20% and creatinine levels in the serum increase to 8 mg/dl. Substantially increased metabolism of normal substrates and a large variety of toxic amines, such as methylamine, dimethylamine, trimethylamine, phenols and indole metabolites also occurs from this bacterial outgrowth. When the small gut bacterial growth increases, there is an increase in ammonia release which then enters the enterohepatic circulation and is converted to urea.
The introduction of renal dialysis has contributed to rapid progress in the clinical treatment of renal failure and elucidation of uremia. When a patient has mild kidney failure where the serum creatinine level is less than 400 xcexcmol/L, the patient does not require renal replacement therapy such as dialysis or renal transplant. However, in general, when the serum creatinine level rises to 900 xcexcmol/L, the patient needs routine dialysis or a kidney transplant to survive.
Dialysis can serve as a lifetime therapy for ESRD patients. Phosphate binders such as calcium acetate, calcium carbonate or aluminum hydroxide are generally prescribed for uremic patients receiving dialysis to reduce elevated phosphate levels. In general, however, dialysis is very expensive, inconvenient, time consuming and may occasionally produce one or more side effects. With a successful kidney transplant, a patient can live a more normal life with less long-term expense. However, there are also high costs associated with transplant surgery, the recovery period and the continuous need for antirejection medications. Further, there is oftentimes a shortage of suitable donors. Accordingly there is a need for alternative strategies.
In the present invention, compositions are provided which comprise a mixture of sorbents selected for their specific adsorption affinities for uremic toxins such as ammonia, urea, creatinine, phenols, indoles, and middle molecular weight molecules. For example, in a preferred embodiment, the mixture of sorbents comprises: oxystarch or oxycellulose with a specific adsorption affinity for urea and ammonia; locust bean gum with a specific adsorption affinity for creatinine and urea; and activated charcoal with a specific adsorption affinity for creatinine guanidines, phenol, Indican and middle molecular weight undefined components. Compositions of the present invention further comprise a bacterial source which metabolizes urea and ammonia, preferably to amino acids which can be used by the bacteria or the patient. Examples of bacterial sources useful in the present invention include, but are not limited, E. coli DH5, Sprosarcina urae and genetically modified yeast cells such as S. pombe. The composition is then enteric coated and/or microencapsulated. Enteric coating of the composition is specifically designed to deliver the sorbents and bacterial source at the ileal and colonic regions of the bowel where maximal resorption of uremic solutes and other molecules are found to occur. This is preferably achieved via an enteric coating material which disintegrates and dissolves at a pH of 7.5 or higher. Examples of enteric coatings with these characteristics include, but are not limited to, Zein, polyglycolactic acid, polylactic acid, polylactide-coglycolide and similar coating materials. Enteric coatings also enable delivery of the sorbents to their site of action in relatively native form without binding of various digestive materials to the sorbents prior to reaching the target region. Alternatively, or in addition, the compositions of the present invention can be microencapsulated thus permitting the compositions to perform like microscopic dialysis units as described by Chang, T. M. S. (Artificial Cells, Chapter 5, in Biomedical Applications of Microencapsulation, edited by Lim, F. CRC Press Fla., pp 86-100). In this embodiment, the composition is coated with a non-absorbable polymeric compound which permits only small and middle-sized molecules into the core wherein the mixture of solvent and bacterial source are located. Examples of non-absorbable polymeric coatings for microencapsulation include, but are not limited to, alginate/alginic acid, chitosan, cellulose acetate pthalate, hydroxyethyl cellulose and similar coating materials. Microencapsulation prevents the binding of macromolecules and other digestive materials which substantially reduce the efficacy of the sorbents to specifically adsorb the uremic solutes to the sorbents of the mixture. The microcapsules pass through the bowel, with the mixture of sorbents adsorbing multiple uremic solutes and the bacterial source metabolizing urea and ammonia and urea, and are then excreted intact from the bowel. Thus, in this embodiment, the patient is protected from the possibility of microbial infection by the bacterial source as the bacterial source is kept within the microcapsule. Accordingly, in a preferred embodiment, compositions of the present invention are both microencapsulated and enteric coated.
Compositions of the present invention may further comprise a phosphate binding agent such as aluminium hydroxide, calcium carbonate or calcium acetate and a water binding agent such as psyllium fibers, naturally occurring gums or modified starches.
Compositions of the present invention are administered orally to patients with uremia to alleviate the symptoms of uremia. By xe2x80x9calleviation of symptomsxe2x80x9d of uremia, it is meant that the composition removes sufficient levels of uremic toxins such that a patient suffering from uremia either does not require dialysis, requires dialysis less frequently or for shorter durations, or does not require initiation of dialysis as soon.
In a preferred embodiment, oral delivery of the mixture of sorbents in the composition will be accomplished via a 2 to 4 ounce emulsion or paste mixed with an easy to eat food such as a milk shake or yogurt. The microencapsulated bacterial source can be administered along with the mixture of sorbents in the emulsion or paste or separately in a swallowable gelatin capsule.
A mathematical model of solute transport of oral sorbents has been developed based on the diffusion controlled solute flux into the intestinal lumen followed by physical binding or chemical trapping (Gotch et al. Journal of Dialysis 1976-1977 1(2):105-144). This model provides the theoretical basis of solute removal through the gut.
For example, gut clearance of urea is 10 to 12 ml/minute in normal renal function and is reduced to 3 to 4 ml/minute in patients with severely reduced renal function. This reduction in the clearance rate is independent of blood urea concentration and directly related to impaired renal function. The normal creatinine clearance rate is 2 to 5 ml/minute.
Further, at steady state, as rate of mass generation is equal to rate of mass elimination, the first order sorbent promoted gut clearance of any solute is given by the mass balance equation:
Gs=(Kr+Kg)Cs, 
where Gs=rate of solute generated, Kr=rate of renal clearance, Kg=rate of gut clearance and Cs is concentration of solute.
The process of sorbent binding, for a given amount of sorbent, is saturable. Thus, below the saturation levels, as the rate of gut clearance of the solute is first order, the above equation can be depicted as:
Cs=Gs/(Kr+Kg). 
Above the saturation levels, as the rate of gut clearance is zero, the equation can be rewritten as:
Cs=(Gsxe2x88x92sorbent capacity)/Kr. 
These equations are useful in predicting the efficacy of solute removal from the gut based in vitro studies.
In fact, this model was applied to Friedman""s data on urea elimination by the gut in uremic patients using oxystarch oral sorbent (Friedman et al. Trans. Am. Soc. Artif. Intern. Organs 1974 20:161-167). With these data, the model showed that maximum sorbent capacity for native oxystarch oral sorbent was 1.5 g/day which is insufficient to replace dialysis or reduce the frequency of dialysis. This model also predicted that for the same patient data, at a protein catabolic rate of 0.95 grams/kg/24 hours and a urea generation of 5 mg/minute, the maximum sorbent capacity of oxystarch should be 7.2 grams of urea nitrogen/day and the gut clearance rate should be 5.6 ml/minute. Sorbent capacity lower than this, such as 5.4 grams of urea/day will at best delay dialysis by months provided the protein catabolic rate can be held at 0.6 grams/kg/24 hours. Thus, this model is useful in determining optimal results for various formulations of compositions of the present invention to alleviate symptoms of uremia in patients.
The following nonlimiting examples are provided to further illustrate the present invention.